Machine tools and processing methods

Abstract

To enable suppression of chattering vibration without degrading machining accuracy or damaging a cutting tool.SOLUTION: A combined machining machine for performing machining by rotating a tool and a workpiece has a parallel plate spring structure 50 including a pair of plate springs 51 and 51 parallel to each other with a through-hole 52 between in an arbor 5B of a cutter 6 for machining the workpiece. Chattering vibration can be suppressed by providing anisotropy to rigidity in a sectional direction orthogonal to a tool axis to change a specific frequency.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a machine tool capable of processing a workpiece into a desired shape such as a gear while suppressing chatter vibration, and a processing method using the machine tool.

Background Art

[0002] In cutting, chatter vibration occurs when the dynamic characteristics of the machine tool, tool, and workpiece and the cutting process satisfy certain conditions. Therefore, it is known that chatter vibration can be suppressed by varying or changing the spindle rotation speed. For example, as a processing method for suppressing chatter vibration in gear processing, Patent Document 1 proposes an invention in which chatter vibration is suppressed by varying the synchronous rotation speed between the workpiece and the cutter. Further, in Patent Document 2, when chatter vibration occurs, cutting is performed while accelerating or decelerating the rotational speed of the gear cutting tool with a depth of cut larger than that at the time when chatter vibration occurred, and processing is performed in a state where chatter vibration is generated. When the amount of variation in the frequency of the gear cutting tool exceeds a predetermined amount, an invention is proposed in which cutting is performed again at that rotational speed to finally obtain a good product.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the case of the invention of Patent Document 1, since the synchronous rotation speed between the workpiece and the cutter is varied, there is a risk that the error of synchronous rotation becomes large, the processed surface becomes wavy, and the processing accuracy deteriorates. In the case of the invention of Patent Document 2, in order to suppress chattering vibration, it is necessary to deliberately generate chattering vibration to search for the optimum rotational speed, which may cause damage to the cutting tool.

[0005] Therefore, an object of the present disclosure is to provide a machine tool and a machining method capable of suppressing chattering vibration without deteriorating machining accuracy or damaging the tool.

Means for Solving the Problems

[0006] To achieve the above object, a first configuration of the present disclosure is A work is held on a spindle that is rotationally driven, and a tool that has a plurality of blades on its outer periphery and is rotationally driven is arranged such that the tool axis is inclined with respect to the spindle axis. While the work and the tool are synchronously rotated, the tool is moved in the direction of the spindle axis a machine tool capable of machining the workpiece to a gear characterized in that a natural frequency changing means capable of changing the natural frequency before or during machining is provided on the tool or a support portion that supports the tool. and changes the natural frequency. and The natural frequency changing means makes the tool have anisotropy in rigidity in the cross-sectional direction orthogonal to the tool axis before machining Another aspect of the first configuration of the present disclosure is that, in the above configuration, the anisotropy of the rigidity is imparted by forming a plurality of leaf spring portions parallel to each other in the tool. Another aspect of the first configuration of the present disclosure is that, in the above configuration, the natural frequency changing means changes the preload on a bearing that supports a rotating shaft on which the tool is mounted in the support portion during machining to change the rigidity of the rotating shaft, thereby changing the natural frequency. At the same time, the number of blades of the tool or the number of anisotropic modes is set such that the ratio of the number of teeth to be machined on the work to the number of blades of the tool does not become the number of anisotropic modes Another aspect of the first configuration of the present disclosure is that, in the above configuration, the natural frequency changing means changes the pressure in a pressure chamber provided in the tool during machining to change the rigidity of the tool, thereby changing the natural frequency. A work is held on a spindle that is rotationally driven, and a tool that has a plurality of blades on its outer periphery and is rotationally driven is arranged such that the tool axis is inclined with respect to the spindle axis. While the work and the tool are synchronously rotated, the tool is moved in the direction of the spindle axis to a gear To achieve the above object, a second configuration of the present disclosure is a method of machining the workpiece using a machine tool In the tool, by making the tool have anisotropy in rigidity in the cross-sectional direction orthogonal to the tool axis, the tool characterized by changing the natural frequency of and performing machining. ​​​

Advantages of the Invention

[0007] According to the present disclosure, chatter vibration can be suppressed by changing the natural frequency of the tool and / or the support portion that supports the tool. Further, since the synchronous rotation speed between the workpiece and the tool does not vary, the error in synchronous rotation is reduced and the machining accuracy does not deteriorate. Furthermore, since there is no need to generate chatter vibration, the tool is not damaged.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

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Figure 10

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing the configuration of gear machining by a composite machining machine, which is an example of a machine tool according to the present disclosure. The composite machining machine 1 has a chuck 3 for holding a workpiece W on a spindle 2 that is rotationally driven. A cutter 6 is fixedly attached to a tool post 4 via an arbor 5 so as to be rotationally driven. The arbor 5 and the cutter 6 serve as the tools of the present disclosure. FIG. 2 shows a structure for giving anisotropy in rigidity to the cutter 6. As shown in FIG. 2(A), a commercially available arbor 5 (hereinafter referred to as "5A" for distinction) has the same rigidity because the cross-sectional shape along the line A-A is the same in the I direction and the II direction. On the other hand, in the arbor 5 shown in FIG. 2(B) (hereinafter referred to as "5B" for distinction), a parallel plate spring structure 50 is provided in a part of the shank portion. The parallel plate spring structure 50 is provided with a pair of plate spring portions 51, 51 that are parallel to each other with a through hole 52 penetrating in the II direction therebetween. Recesses 53 are respectively formed on the outer sides in the I direction of the respective plate spring portions 51. By providing the parallel plate spring structure 50 in this way, the arbor 5B has different cross-sectional shapes along the line B-B in the I direction and the II direction, and thus different rigidities.

[0010] FIG. 3 is a diagram showing the transfer function of the cutter 6. The transfer function 11 (shown by a dotted line) of the cutter 6 fixed to the arbor 5A in FIG. 2(A) has one natural frequency because the rigidity is the same in the I direction and the II direction. On the other hand, the transfer function 12 (shown by a solid line) of the cutter 6 fixed to the arbor 5B in FIG. 2(B) has two natural frequencies in the I direction and the II direction because the rigidity is different in the I direction and the II direction. FIG. 4 is a diagram showing the phase relationship between the workpiece W and the cutter 6. When gear machining is performed with the cutter 6 provided with the parallel plate spring structure 50 in FIG. 2(B), as shown in FIG. 4(A), the cutter 6 is machining in the I direction at the machining point (black circle) before one rotation of the workpiece W. However, when the workpiece W is in the state of FIG. 4(B) after one rotation from FIG. 4(A), the cutter 6 is machining in the II direction at the machining point (black circle).

[0011] FIG. 5 is a diagram showing the machining theory for suppressing chatter vibration in the compound machining machine 1. FIG. 5 is a view of the cutter 6 machining a gear as seen from the side, showing the situation where the cutting edge 61 of the cutter is machining from the tooth bottom surface 22 toward the tooth tip surface 21. Also, the distance between the machining surface 23 before one rotation shown by the two-dot chain line and the current machining surface 24 shown by the solid line is the cut thickness 25. When machining with the cutter 6 of the commercially available arbor 5A as shown in FIG. 2(A), since the natural frequency of the cutter 6 does not change as shown in FIG. 5(A), the unevenness of the machining surface 23 before one rotation and the current machining surface 24 has the same frequency, so the cut thickness 25 changes periodically and chatter vibration occurs. On the other hand, when machining with the cutter 6 of the arbor 5B provided with the parallel plate spring structure 50 as shown in FIG. 2(B), since the natural frequency of the cutter 6 changes as shown in FIG. 5(B), the unevenness of the machining surface 23 before one rotation and the current machining surface 24 has different frequencies, so the cut thickness 25 becomes irregular and chatter vibration is suppressed.

[0012] When the above parallel plate spring structure 50 is adopted, in order to enhance the effect of suppressing chatter vibration, it is desirable to determine the number of blades of the cutter 6 or the anisotropic mode number so that the ratio of the number of teeth of the work W to the number of blades of the cutter 6 does not become an anisotropic mode number. FIG. 6 is a flowchart for determining the number of blades of the cutter 6 or the anisotropic mode number of the cutter rigidity. First, in step (hereinafter referred to as "S") 1, the number of teeth of the work W is obtained. In S2, the number of blades of the cutter 6 or the anisotropic mode number is determined. In S3, the ratio of the number of teeth of the work W to the number of blades of the cutter 6 and the anisotropic mode number are compared. If the two are equal (including the case of approximately equal), return to S2 and reset the number of blades of the cutter 6 or the anisotropic mode number, and if the two are not equal, end.

[0013] Thus, according to the compound machining machine 1 and the machining method of the above form, in a case where a tool composed of the arbor 5B and the cutter 6 and the work W can be rotated to machine the work W, the arbor 5B of the cutter 6 is provided with the parallel plate spring structure 50 (natural frequency changing means) capable of changing the natural frequency before machining, so that chatter vibration can be suppressed without deteriorating the machining accuracy or damaging the tool. In particular, since the natural frequency changing means changes the natural frequency before machining by imparting anisotropy to the rigidity in the cross-sectional direction orthogonal to the tool axis in the arbor 5B, it is possible to easily change the natural frequency by using the arbor 5B. Also, since the anisotropy of rigidity is imparted by forming leaf spring portions 51, 51 parallel to each other in the arbor 5B, anisotropy can be easily imparted by forming the leaf spring portions 51, 51.

[0014] Hereinafter, a modification example of the present disclosure will be described. FIG. 7 shows a structure in which a natural frequency changing means is provided in a tool post 4 which is a support portion to which the arbor 5 is attached in the complex machining machine 1. Here, a hydraulic chamber 7 is provided in the rotary shaft 4a portion of the tool post 4, and the preload of the rolling bearing 10 is changed by pressurizing or depressurizing the hydraulic chamber 7 by a hydraulic unit 8, so that the rigidity of the rotary shaft 4a can be changed during machining to change the natural frequency. The change in the natural frequency is performed by calculating the pressurization and depressurization cycles based on the rotation speed command from the tool rotation speed control unit 9 and controlling the hydraulic unit 8. FIG. 8 shows a structure in which a natural frequency changing means is provided in the arbor 5. Here, a hydraulic chamber 7 is provided in the shank portion of the arbor 5, and the natural frequency can be changed by changing the number of anisotropic modes of rigidity in the cutter 6 during machining by pressurizing or depressurizing the hydraulic chamber 7 by a hydraulic unit 8. The change in the natural frequency is performed by calculating the pressurization and depressurization cycles based on the rotation speed command from the tool rotation speed control unit 9 and controlling the hydraulic unit 8.

[0015] Further, the present disclosure is not limited to machining in which both the tool and the workpiece are rotated as in the above-described embodiment. FIG. 9 shows a structure in which a means for changing the natural frequency is provided for an end mill as a tool. As shown in FIG. 9(A), for a commercially available end mill 70 (hereinafter referred to as "70A" for distinction), since the cross-sectional shape in the A-A direction is the same in the I direction and the II direction, the rigidity is the same. On the other hand, as shown in FIG. 9(B), by providing a parallel plate spring structure 50 similar to the arbor 5B on a part of the shank portion of the end mill 70 (hereinafter referred to as "70B" for distinction), since the cross-sectional shape in the B-B direction is different in the I direction and the II direction, the rigidity is different. FIG. 10 is a diagram showing the machining theory for suppressing chatter vibration in milling. FIG. 10 is a view from above of the state where the end mill is machining the side surface of the work W, and the tool edge 601 is performing up-cut (down-cut is also possible) from the finished surface 202 toward the stock surface 201. Also, the distance between the machining surface 203 before one cutting edge shown by the two-dot chain line and the current machining surface 204 shown by the solid line is the cutting thickness 205. When machining with the end mill 70A, since the natural frequency of the end mill 70A does not change, as shown in FIG. 10(A), since the unevenness of the machining surface 203 before one cutting edge and the current machining surface 204 has the same frequency, the cutting thickness 205 changes periodically, and chatter vibration occurs. On the other hand, when machining with the end mill 70B provided with the parallel plate spring structure 50, anisotropy is imparted to the rigidity and the natural frequency of the end mill 70B changes. Therefore, as shown in FIG. 10(B), since the unevenness of the machining surface 203 before one cutting edge and the current machining surface 204 has different frequencies, the cutting thickness 205 becomes irregular, and chatter vibration is suppressed.

[0016] Note that in the arbor 5B and the end mill 70B of the above embodiment, the parallel plate spring structure is not limited to the above structure. For example, the number of plate spring portions may be three or more instead of a pair, and the outer recess may not be provided. Also, in the above embodiment, examples of performing machining by rotating the tool and the work and examples of performing machining on the work by rotating the tool are given, but the present disclosure can also be applied to a case where the work is fixed to the rotation axis and machining is performed without rotating the tool. Therefore, the work is not limited to a gear. A plurality of natural frequency changing means can also be adopted. For example, a combination such as providing a parallel plate spring structure or a hydraulic chamber in the tool to impart anisotropy of rigidity and providing a hydraulic chamber for changing the preload of the bearing on the tool post can be considered.

Explanation of Signs

[0017] 1... machining center, 2... spindle, 3... chuck, 4... tool post, 4a... rotating shaft, 5... arbor, 6... cutter, 7... hydraulic chamber, 8... hydraulic unit, 9... tool rotational speed control unit, 10... rolling bearing, 50... parallel plate spring structure, 51... leaf spring portion, 52... through hole, 53... recess, 70... end mill, 601... tool cutting edge, W... workpiece.

Claims

1. A machine tool capable of machining a gear by holding a workpiece on a rotating spindle and arranging a rotating tool having a plurality of blades on its outer periphery such that the tool axis is inclined relative to the spindle axis, and moving the tool in the direction of the spindle axis while rotating the workpiece and the tool synchronously, comprising: A natural frequency changing means capable of changing a natural frequency before or during machining is provided on the tool or a support portion that supports the tool, The machine tool, characterized in that the natural frequency changing means changes the natural frequency of the tool before machining by imparting anisotropy to the rigidity of the tool in a cross-sectional direction perpendicular to the tool axis.

2. The machine tool according to claim 1, characterized in that the anisotropy of rigidity is imparted by forming a plurality of parallel leaf spring portions within the tool, and the number of teeth of the tool or the number of modes of the anisotropy is set so that the ratio between the number of teeth to be machined on the workpiece and the number of teeth of the tool does not become the number of modes of the anisotropy.

3. 3. The machine tool according to claim 1, wherein the natural frequency changing means changes a preload on a bearing that supports a rotating shaft to which the tool is attached within the support portion during machining to change the rigidity of the rotating shaft, thereby changing the natural frequency.

4. 3. The machine tool according to claim 1, wherein the natural frequency changing means changes the natural frequency by changing the pressure in a pressure chamber provided within the tool during machining to change the rigidity of the tool.

5. A method for machining a workpiece into a gear by using a machine tool in which a workpiece is held on a rotating spindle, a rotating tool having a plurality of blades on its outer periphery is arranged so that the tool axis is inclined with respect to the spindle axis, and the workpiece and the tool are rotated synchronously while the tool is moved in the direction of the spindle axis, A machining method characterized in that machining is performed by changing the natural frequency of the tool before machining by imparting anisotropy to the rigidity of the tool in a cross-sectional direction perpendicular to the tool axis.

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